The present invention relates to a data processing system for converting from logical addresses to physical addresses.
The invention relates to a data processing system utilizing a page address system and is intended to smoothen the processing of the address conversion from a logical address to a physical address when a memory area is commonly used for several application purposes, program or job. More particularly, the system of the invention simplifies the processing when changing the physical address of a page commonly used.
In general, the memory of the data processing system is designed for improved cost performance by utilizing the hierarchical structure of the main memory unit at high speed, but small capacity, and an auxiliary memory unit at low speed, but large capacity. In such case, various types of data are transferred from the auxiliary memory unit, and stored, as required, in a specific physical address in the main memory unit. In other words, correspondence of several logical addresses is necessary.
Thus, the memory areas are classified into blocks, each of which is known as a page, for every predetermined size, for example, one thousand words. The pages are utilized to prepare a correspondence table or page map, of the physical address of the main memory unit and the logical address of the program. Furthermore, an address conversion for converting the logical address to the physical address is prepared, and access to the main memory unit is specifically provided after the address conversion. This method is called the page address system.
In the page address system, the program, even if it is described on continuous pages of the logical addresses, may be used by storing it on the non-continuous and desired pages of the physical addresses. It is thus possible to extract the necessary pages from the auxiliary memory unit and transfer them to idle pages at desired physical addresses of the main memory unit. The memory capacity viewed from the program may be expanded, irrespective of the capacity of the main memory unit, only by making the capacity of the auxiliary memory unit large.
On the other hand, when a data processing system is commonly used by several processing programs or jobs, it is conceived that the basic control program be commonly used by each processing program. In such case, since the space of logical addresses is independent in each program, a page map must be prepared for each processing program. In the aforedescribed memory unit with a hierarchical structure, the pages which are considered to be used for a while are left, but the old pages are ruled out. Newly required pages are then transferred from the auxiliary memory unit to the areas of the old pages.
The probability of usage is judged on the basis of an experience rule. The rule is that there is a high probability of continuous use of data of the continuous addresses. That is, there is a high probability of continuous use of newly transferred pages, but a low probability of use of the old pages. In such a judging method, when a page which has once been extracted is again transferred to the main memory unit for meeting the necessity, it is not always returned to the initial position. Therefore, the physical address of the page map area, or entries, concerning the relevant page must be rewritten.
When considering here the pages commonly used by several programs, as hereinbefore mentioned, it is necessary, in order to change the physical addresses, to rewrite all the several page map areas corresponding to the physical address. The more the number of programs commonly used, the more important this problem, and the longer and longer the time taken for rewriting of the map area.
The principal object of the invention is to provide a data processing system which smoothly processes the address conversion from a logical address to a physical address.
An object of the invention is to provide a data processing system which provides a simplified process for changing the physical address of a page commonly used.
Another object of the invention is to provide a data processing system of simple structure, which is inexpensive in manufacture.
Still another object of the invention is to provide a data processing system which operates rapidly, using a small number of components, for converting addresses from logical to physical.
Yet another object of the invention is to provide a data processing system which functions efficiently, effectively, reliably, rapidly and economically.